The present invention relates to a method of preparing boron modified hydropolysilazane polymers. The method comprises reacting a hydropolysilazane polymer with borane for a time sufficient to produce the desired polymer. This invention also relates to the novel polymers produced by the above process.
A variety of polysilazane oligomers. cyclics. resins and linear polymers are known in the art. Generally, such polymers are characterized as having backbones with alternating silicon and nitrogen atoms. Cannady, in U.S. Pat. No. 4,540,803 issued Sep. 10, 1985. described a novel class of silazane polymers (hydropolysilazanes) having a three-dimensional structure formed by the presence of HSiN.sub.3 and R.sub.3 SiNH groups. This unique structure afforded such polymers physical properties which are desirable in the formation of various ceramic materials.
Boron modified polysilazane polymers and various methods for their preparation are also known in the art. For instance, U.S. Pat. No. 5,030,744 granted to Funayama et al. describes the formation of boron modified polysilazanes by reacting a polysilazane having repeating units comprising: ##STR1## with a boron compound. The polysilazanes described in this reference, however, differ from those claimed in the present invention in that those of the reference are primarily linear or cyclic whereas those of the present application are the highly branched, three-dimensional polymers of Cannady, supra. Moreover, the boron is used in the reference to crosslink the polysilazanes and thereby increase their molecular weight whereas borane is used in the present application to merely add a BH.sub.2 group to the hydropolysilazane polymer.
Likewise, European Patent No. 364.323. U.S. Pat. No. 4,910,173 granted to Niebylski and Seyferth et al., J. Am. Ceram. Soc. 73, 2131-2133 (1990), describe various other methods of forming boron modified polysilazane polymers. These references teach reacting a polysilazane with a trihalogen borane, a boroxine or a borane, respectively. As with the Funayama patent described above, however, these references do not describe the polysilazanes of the present invention.
Therefore, what has not been described in the prior art is use of borane to modify the specific polymers claimed herein. The present inventor has discovered that such polymers have properties superior to those known in the art.